This one's kind of "out there", but unbeatable if you'd like to take the organic, from-the-heart, not-the-head kind of approach: Robert Olen Butler's From Where You Dream: The Process of Writing Fiction. Rather than old-fashioned, technique-based instruction, Butler really encourages you to go to your "dream space" (almost becoming the character) to the point where you are walking around in your fictional world. You will soon "discover", he says, what is supposed to naturally happen next.

Another excellent one, which is more practical and down-to-earth: Ron Carlson Writes a Story. I love this one not just because it's a short read, but because Carlson actually takes you through pretty much the exact thought process he used to write one of his most popular stories. He pauses and tells you what he was thinking at each moment of the story-writing process, and tells you where he added content, debated about character choices, etc. One of the most unique elements of this book though, is that he also gives tips about your external environment, not just the story itself. He tells you how he got rid of distractions, set himself up in a good place to begin writing, and importantly, when he let himself take a break.